In the manufacture of steel in basic oxygen type furnaces (BOF), measurements of bath temperature are desirably taken during the refining period so that adjustments can be made in the oxygen blowing time, rate and volume for the final bath chemistry, and temperature. During the oxygen blowing process the molten metal bath is very agitated by the blowing of oxygen beneath and onto the surface of the slag and metal. In order to obtain accurate and reliable temperature readings, temperature probes must be immersed well below the surface of the steel bath and steel/slag layer interface. A deep penetration into the steel bath prevents the temperature sensor from being blown around by the high volume high force oxygen discharge from the oxygen lance. Ideally, sensors should be immersed 6 inches or more into the bath below the interface.
Oxygen readings are desirable and possible after a controlled blow is finished or interrupted. Carbon content can be accurately calculated from metal bath oxygen content at levels below the 15% carbon range. Temperature is obtained by the thermocouple of the oxygen probe. The oxygen reading for free oxygen can be used for accurate and precise addition of deoxidation agents.
Using a reliable accurate in-blow temperature probe and oxygen temperature carbon and sample probe, through the BOF furnace aperture results in saving steel making time and furnace wear resulting in more production and better or equivalent quality at lower costs.
Because of the high density of the molten metal, it is difficult to push the probe beyond the slag layer and into the metal to sufficient depth because of the buoyancy afforded by the dense metal displaced by the probe. The most reliable method at the present involves the use of a very expensive sublance with motorized assembly to lower a pipe into the BOF vessel. Because of the expense of several million dollars assembling and installing this sublance equipment in a steel mill, it is not a desirable choice. It also is not a desirable choice because of new steel making procedures using ladle furnaces and ladle metallurgical stations. Accordingly, free falling bomb lances have been devised to weight a probe for immersion purposes. The Cole Patent 3,374,122 is an example of a weighted probe. The Ehrenberg Patent No. 3,497,398 is a further development of the bomb type probe. Patent No. 3,505,871 shows an additional type of immersion vehicle intended to be inserted in a BOF vessel.
These types of drop-in sensors, have not provided consistent and reliable results because of ineffective and inconsistent immersion depths below the slag layer especially while blowing oxygen. Typically there is not enough weight provided to overcome the buoyant force to obtain sufficient penetration for accurate and reliable "in blow" temperature readings and accurate "after blow" oxygen, carbon and temperature readings.